Drop C lowers every string by one whole step and then drops the lowest string another whole step, giving you C G C F A D.
You can use .010 gauge strings in Drop C, but at the lower pitch they can feel loose. At the same pitch and scale length, a heavier gauge feels firmer. Scale length and setup also change how a string feels, so gauge is only part of the choice.
Good starting points are Power Wound Nickel 11–50 (S1150 Medium Light) and Power Wound Nickel 11–56 (S1156 Heavier Bottom), which adds a heavier low end for the dropped 6th string.
Switching to heavier strings or tuning lower can affect neck relief and intonation, so some guitars benefit from small setup adjustments.
If you want a specific feel, you can build a custom combination with single guitar strings. For the full guide, see our Drop C tuning guide.